Method and apparatus for asymetrical optical modulation

Abstract

An optical data transmission system using a Mach Zehnder (M-Z) modulator asymmetrically modulates the optical carrier to generate control information to optimize the transmitted optical signal.

What is claimed is:  
     
       1. A method of biasing an optical modulator comprising the steps of: 
       modulating one or more control tones asymmetrically onto an optical carrier producing an optical data stream;  
       processing said optical data stream to generate an error signal; and  
       adjusting said modulating step as directed by said error signal.  
     
     
       2. The method of  claim 1  wherein said one or more control tones are sinusoidal. 
     
     
       3. The method of  claim 2  wherein said one or more control totes are square waves. 
     
     
       4. The method of  claim 3  wherein said one or more control tones are code words. 
     
     
       5. The methods of claims  1 ,  2 ,  3 , or  4  wherein said processing step further comprises comparing said one or more control tones to said optical data stream. 
     
     
       6. The methods of claims  1 ,  2 ,  3 , or  4  wherein said modulating step modulates said one or more control tones substantially on the ‘0’ level of said optical data stream. 
     
     
       7. The methods of claims  1 ,  2 ,  3 , or  4  wherein said modulating step modulates said one or more control tones substantially on the ‘1’ level of said optical data stream. 
     
     
       8. The methods of claims  1 ,  2 ,  3 , or  4  wherein said modulating step results in the amount of said one or more control tones present on the ‘0’ level of said optical data stream being unequal to the amount of said one or more control tones present on the ‘1’ level of said optical data stream. 
     
     
       9. Tho methods of claims  1 ,  2 ,  3 , or  4  wherein said modulating step results in substantially none of said one or more control tones present on the ‘0’ level of said optical data stream. 
     
     
       10. The methods of claims  1 ,  2 ,  3 , or  4  wherein said modulating step results in substantially none of said one or more control tones present on the ‘1’ level of said optical data stream. 
     
     
       11. A system for biasing an optical modulator comprising: 
       an optical modulator for modulating one or more control tones onto an optical carrier generating an optical data stream;  
       a monitor coupled to said optical data stream and generating an error signal; and  
       a bias generator coupled to said error signal generating a bias signal coupled to said optical modulator.  
     
     
       12. The system of  claim 11  wherein said one or more control tones are sinusoidal. 
     
     
       13. The system of  claim 11  wherein said one or more control tones are square waves. 
     
     
       14. The system of  claim 11  wherein said one or more control tones are code words. 
     
     
       15. The systems of claims  11 ,  12 ,  13 , or  14  wherein said monitor is coupled to said one or more control tones. 
     
     
       16. The systems of clams  11 ,  12 ,  13 , or  14  wherein said optical modulator modulates said one or more control tones substantially on the ‘0’ level of said optical data stream. 
     
     
       17. The systems of clams  11 ,  12 ,  13 , or  14  wherein said optical modulator modulates said one or more control tones substantially on the ‘1’ level of said optical data stream. 
     
     
       18. The systems of claims  11 ,  12 ,  13 , or  14  wherein said optical modulator modulates the amount of said one or more control tones onto the ‘0’ level of said optical data stream substantially unequal to tie amount of said one or more control tones onto the ‘1’ level of said optical data stream. 
     
     
       19. The systems of claims  11 ,  12 ,  13 , or  14  wherein said optical modulator modulates substantially none of said one or more control tones onto the ‘0’ level of said optical data stream. 
     
     
       20. The systems of claims  11 ,  12 ,  13 , or  14  wherein said optical modulator modulates substantially none of said one or more control tones onto the ‘1’ level of said optical data stream.